1. Field of the Invention
The present invention relates to an intermittent feeding apparatus for feeding a continuous sheet that is applicable to a machine for processing a continuous sheet such as a flexorotary press, a flat plate rotary press, a rotary die cutter, a flat plate stamping machine, etc., and more particularly to an intermittent feeding apparatus for feeding a continuous sheet for successively performing printing of a predetermined size at the respective intervals alotted for printing of a roller paper sheet or other continuous sheets with any arbitrary print length within the range of a circumferential dimension of a plate drum of a rotary press printing machine.
2. Description of the Related Art
FIG. 17 shows a rotary press printing machine for a continuous sheet (hereinafter called simply "sheet") that is known in the prior art. With reference to this figure, a roll-shaped sheet 1 has its center portion pivotably supported by an unwinder 2 and is pulled by pull rolls 11 as nipped therebetween. The sheet 1 is unwound in the direction of the arrows and travels towards printing sections 10. The unwound sheet 3 passes between a printing drum 5 and a pressing drum 6 of each printing section 10 via a wrapping roll 4 and is thereby printed. In the illustrated example, three sets of printing sections 10 are shown, but in general there are provided printing sections for three to six colors depending upon the number of colors to be printed. The printed sheet 3 is pulled and pinched by a pair of pull rolls 11, and is then wound onto a roll 12 again by means of a winder 13.
In a printing mechanism shown in FIG. 18, ink 34 within an ink reservoir vessel 8 is transferred onto a surface of a printing plate 14 with the aid of an inking roll 7, and then printing is effected on the surface of the sheet 3. Excessive ink (ink exceeding a necessary amount) on the surface of the inking roll 7 is scraped away by means of a doctor blade 9, and is returned into the ink reservoir vessel 8. It is to be noted that the outer circumferential surface velocities of the pull rolls 11, pressing drum 6 and printing plate 14 are identical so that the traveling velocity of the sheet 3 may coincide with the surface circumferential velocity of the printing plate 14.
Furthermore, a braking device (not shown) for the roll 1 is mounted to the unwinder 2 so that slackening may not arise in the sheet 3 due to the fact that the sheet 3 is unwound to more than a necessary extent because of an inertia of the roll 1. In addition, the winder 13 is provided with a driving device (not shown) for the roll 12 for winding the sheet 3 fed from the pull rolls 11. A print length on a sheet in such a rotary press printing machine is determined by an arc length of the printing plate 14, and the maximum length of this arc length is the circumferential length .pi.D of the printing plate 14, where D represents the outer diameter of the printing plate 14.
Thus, the repeated print length is determined by the arc length of the printing plate 14, and in the case where the print length is smaller than the circumferential length .pi.D of the printing plate 14, blank portions where printing is not effected would be produced. These blank portions are quite unnecessary, and so, they are cut and thrown away in the subsequent step after the printing and winding. Accordingly, in the heretofore known machines, for the purpose of reducing these blank portions, the following proposals were made:
(I) A method of varying the outer diameter (D) of the plate drum 5 depending upon a print length, that is, a method of replacing the plate drum 5, was proposed.
(II) A method of vertically moving either the upper or lower roll rotating at a constant velocity depending upon a print length as shown in FIG. 19, was proposed. In the example illustrated in FIG. 19, during the period when the lower pull roll is raised the pull rolls nip the sheet to pull it, while during the period when the lower pull roll is lowered, the sheet stops. In other words, since printing is effected only when the sheet is traveling, a method of intermittently feeding a sheet in which the timing for raising and lowing the pull roll is varied depending upon a desired print length, was proposed.
(III) A method of intermittently feeding a sheet, in which a pulling member 35 for the sheet 3 is attached to one of the pull rolls 11 as shown in FIG. 20, the surface circumferential velocity of this pulling member 35 is made identical to the surface circumferential velocity of the printing plate 14, and further the arc length of the pulling member 35 is made larger than the arc length of the printing plate 14, was proposed.
While the above-described counter-measures (I), (II) and (III) have been heretofore proposed, they respectively involved the following problems:
Although the method (I) is a method which has been most commonly practiced, it has shortcomings that the replacement work for the plate drum which must be carried out each time a print length is varied, is troublesome and the printing mechanism is complex, and further, the largest shortcoming is that expensive plate drums having as many different circumferential as desired must be prepared, and hence a manufacturing cost of a printed sheet becomes high.
The method (II) is an improved counter-measure for eliminating the shortcoming of the method (I) (replacement of a plate drum being unnecessary). However, it also has shortcomings that since the sheet is pulled while being nipped between the pull rolls, a printed surface of a sheet which has been printed in the preceding step would be pressed by the pull roll, and hence ink which has either not yet been dried or not yet adhered to the surface of the sheet perfectly would be removed by the pull roll, or in some cases the printed surface of the sheet would be contaminated by the ink adhered to the surface of the pull roll. Moreover the vertically moving roll having a large inertia at a high frequency would result in mechanically unreasonable operations, which cause mechanical vibrations, and hence cannot operate properly in a high speed operation of the machine.
The method (III) is also an improved counter-measure for eliminating the shortcoming of the method (I) (replacement of a plate drum being unnecessary). However, since the sheet is pulled while being nipped similarly to the method (II), in this respect the method (III) has the similar shortcomings as does the method (II). In addition, it is necessary to replace the pulling member each time the print length is varied, hence pulling members having as many different arc lengths as desired need to be prepared, and so, this method has the same shortcoming as the method (I).
Furthermore, in the case where the pulling member is made of plastics, rubber, etc., there was a problem in durability, mainly in durability against abrasion (lowering of a sheet pulling force and reduction of a pulling dimension caused by abrasion, especially variation in the amount of slip when momentarily accelerating a stationary sheet would be directly related to the variety of repeat lengths of a sheet). In addition, there was a problem to be resolved upon practically embodying the method such that in the case of making the pulling member of metal, since high precision manufacturing is required, the manufacturing cost would become high.